Semiconductor devices, such as microprocessor dies, are typically mounted in a package and attached to a printed circuit board (PCB), such as a motherboard, through a socket. The socket interfaces with connections on the package to distribute power to and signals from the package (and the semiconductor device) to other devices. Several technologies exist for making connections between the socket and the package, including pin grid array (PGA), ball grid array (BGA), and land grid array (LGA).
LGA sockets include spring-loaded contacts to interface with conductive pads on a packaged semiconductor device. The socket may be soldered onto a motherboard with BGA contacts (e.g., solder balls) under the socket. The spring-loaded contacts create pressure against the pads of the package when the package is inserted into the socket. This pressure assures reliable electric connection between the motherboard and the package. When an LGA contact is pressed the package is inserted into the socket, the tip of the contact wipes a certain distance along the landing pad surface of the package.
FIG. 1 illustrates an LGA socket. The socket 100 includes several contacts divided into two L-shaped regions 102 and 104. The two regions 102 and 104 may include contacts having different orientations (relative to a socket sidewall 106) to obtain enough deflection working range and to avoid electrical shorting. The wiping angle of contacts in each of the two regions 102 and 104 may be represented by the two arrows 108 and 110, respectively. A package is inserted into the socket 100 and the contacts in the regions 102 and 104 make contact with pads on the package to create electrical connections with the semiconductor device encased in the package.
The wiping of the contacts onto the pads creates friction that may twist an installed package. Using some designs, the resulting torque could be as high as 6 lbs-in. This may result in a misalignment of the package during assembly or damage the solder balls under the socket 100. For example, the excessive torque can weaken solder joints connecting the contacts to the socket 100. Alignment pins 112, which attach to the installed package, may be used to reduce the force generated by the contacts, or the socket housing may be constructed from thicker and stronger material. However, these additions may significantly increase the cost of the package 100.